Rotary drilling rigs for forming boreholes require a rotary table centrally positioned on the floor of the drilling rig. The rotary table has a rotating center which receives a kelly bushing therein which imparts rotation into a kelly. The kelly is free to slide within the bushing and has a string of drill pipe connected at the lower end and a swivel at the upper end thereof.
The rotating table center and kelly bushing usually have bolt heads, fastener heads, and various other protrusions as well as various different indentions formed thereon. This is especially so on the older rotary drilling rigs.
The roughnecks working on the confined floor of a drilling rig must handle cables, chains, ropes, water hoses, and various hand and power tools. All of this is carried out in an extremely small floor area and from time to time a tool will inadvertently fall onto the rotating table center and centrifugal force throws the tool outwardly where it may strike a workman.
Now and then a roughneck will accidently get the end of a chain, rope, or hose caught in the rotary, which usually results in a fatal injury.
Drillers and pushers take great care to protect their roughnecks but they cannot always prevent one from entangling a piece of equipment in the inherently dangerous rotating mass of the drilling rig.
Accordingly, it is advantageous and highly desirable to encapsulate the rotary table of a drilling rig so as to isolate this dangerous area from the workmen so that should one accidently drop anything on the rig floor, it cannot possibly be caught in the rotating center.